Apparatus for elasticizing thermoplastic monofilament yarn



March 20, 1962 c. G. EVANS 3,025,584

APPARATUS FOR ELASTICIZING THERMOPLASTIC MONOF'ILAMENT YARN Filed Dec. 30, 1955 2 Sheets-Sheet 1 INVENTOR. Fla 2 CYRILG.EVANS BY MM? MM ATTORNEY nine vaa r.

This invention relates to improved, non-torsionally elasticized yarns and to processes and apparatus for producing the same.

It is well known in the art that, under proper conditions, passing a thermoplastic yarn under tension through a linear path having a sharply angular portion will impart a generally permanent tendency to coil to the yarn. According to conventional prior art practice, the angular portion of the yarn path is provided by passing the yarn in an angular manner about a straight edge, such as is provided by a common razor blade, and processes employing a straight edge for yarn elastization constitute a part of the subicct matter of U.S. applications, Serial Number 274,358, filed March 1, 1952 and Serial Number 522,156, filed July 14, 1955, now abandoned. Such methods are especially advantageous for monofilamcnt yarns since they are capable of producing elasticized yarns which are substantially devoid of all except local torsional stresses and such yarn can be readily employed, without plying, for knitting hosiery and the like on a single carrier machine.

While all of the mechanisms involved in edge-elasticizing processes are not fully understood, it is known that passing a monofilament yarn over a straight edge results in differential transverse stresses being created in the yarn and that it is from a release of these stresses that the elasticized yarn derives its tendency to coil and its elastic nature. Passing a monofilament yarn about a straight edge also results in a cross sectional deformation of the filament with a flattening of one side thereof and in some instances this flattening occurs to the extent that the yarn filament becomes crescent shaped in cross section. It has previously been assumed that this cross sectional deformation of the yarn is an inherent characteristic of the process and that it is necessary for a high degree of elastization.

It has now been found that cross sectional deformation of a monofilament yarn in an edge-clasticizing process can be substantially avoided, that cross sectional deformation is not necessary for imparting excellent elasticity to a monofilament yarn, and that edge elasticized monofilament yarn with a generally cylindrical cross section has several unexpected advantages. According to this invention a running length of monofilament yarn is passed under tension through a linear path having an acutely angular portion and the yarn is at least partially confined during its passage through said angular portion so that it is forced to retain a generally cylindrical cross sect-ion. The means for confining the yarn during its passage through the angular portion of the yarn path preferably comprises a member having an opening therein to receive the yarn with one side of the opening providing a yarn engaging surface, arcuate in a plurality of planes, to be positioned at the apex of the angle in the yarn path. The curvature of the yarn engaging surface in one plane is such that the yarn is forced to retain a generally circular cross section while the curvature of the yarn engaging surface, in planes perpendicular to said one plane, is such that the yarn is properly stressed for purposes of elastization.

A yarn according to this invention has several advantages which result in a more uniform fabric having atent ice a better appearance. In the first place, the new yarns can be passed through a guide or the like Without resulting in an accumulation of twist. When prior art edge elasticized monofilament yarns are passed through a guide or the like, the flat side of the filament prevents the yarn from turning freely within the guide eye so that there is an accumulation of twist on the entry side of the guide until sutficient torque is developed to cause a large part or all of the twist to pass and this results in an uneven distribution of the twist on the exit side of the guide. This is a serious disadvantage in most applications and, for example, when prior art edge-elasticized monofilament yarns are employed in the knitting of ladies hosiery, the uneven twist distribution results in clearly visible bands at intervals along the length of the stocking. With the new yarns of this invention, which have a generally round cross section, there is no accumulation of twist as the yarn is passed through a guide or the like and the twist distribution in the yarn remains substantially uniform. Another disadvantage of prior art edge-elasticized monofilament yarn is that fabrics Woven therefrom frequently exhibit an undesirable sheen, at least in certain areas. It has been found that this undesirable sheen results from the distorted cross section of the yarn and that the more the cross section of the yarn is deformed in passing about the blade edge, the greater the sheen. Inasmuch as the extent of the cross sectional deformation in prior art processes depends upon a number of variables which cannot be precisely controlled, it has not been possible to produce fabrics having a uniform sheen. The monofilament yarns of this invention with their generally circular cross section result in fabrics having a very dull and uniform appearance.

To obtain the above advantages, the yarn need not have a completely circular cross section but need only have a cross section which is generally circular. By generally circular it is meant that not more than about 15% of the peripheral surface is flattened to the extent that it has a radius of curvature appreciably above the mean radius of curvature of the peripheral surface of the yarn and that the minimum diameter of the yarn is at least about of the maximum diameter. If the cross sectional configuration of the yarn is controlled so that it at least conforms to these limits, the yarn is substantially devoid of the disadvantages of prior art edge elasticized yarns.

The invention will now be described with reference to the accompanying drawings in which:

FIGURE 1 is a schematic view in perspective of one form of apparatus suitable for making the improved yarns of this invention.

FIGURE 2 is an enlarged top plan view of the yarn engaging portion of the blade member employed in the apparatus of FIGURE 1.

FIGURE 3 is an edge view of the yarn engaging portion of the blade member as it would appear looking from the top of FIGURE 2 of the drawings.

FIGURE 4 is a cross sectional view of a portion of the blade member taken along the line 44 of FIGURE 2 of the drawings.

FIGURE 5 is a cross sectional view of a portionbf a modified type of blade member suitable for use in the apparatus of FIGURE 1.

FIGURE 6 is a cross sectional view of several prior art edge-elasticized monofilaments.

FIGURE 7 is a cross sectional view of several monofilaments according to this invention.

With particular reference to FIGURES l to 4 of the drawings, there is illustrated a yarn supply means 10 mounted on a suitable frame or support member, not illustrated. A yarn end, indicated by the reference numeral 12, is led from supply package It? through a guide eye 14, about a tension regulating device 16 and then to a blade assembly generally indicated by the refer nce numeral 18. The tension regulating device 16 serves the dual purpose of removing the fluctuations in tension resulting from the removal of the yarn from the supply package 10 and of supplying the yarn end to the blade assembly 18 at a proper tension, while the guide 14 permits the yarn to be removed from supply package 10 in an over-end manner. From the blade assembly 18, which will subsequently be described in greater detall, the yarn is drawn through a portion of the yarn path at 20 having a relatively greater radius of curvature and is then passed through a guide 22 to a pair of driven rolls 24. The yarn is then passed through a guide 25 and to a conventional takeup means 26 here illustrated as comprising a ring and spindle array.

The blade assembly, generally indicated by the reference numeral 18 is illustrated as comprising an arcuate heater strip 28 which has been bent to a radius of about 4 inches in order to present slightly curved surface to the yarn. The heater strip 28 is adapted to be heated by means of an electric current passed therethrough and is connected by a pair of electrical conductors 30 and 32 to a variable transformer 34 which is supplied with power from any suitable source, not illustrated, through leads 36 and 38. Mounted on heater strip 28 by means of a holder 40 is a blade member 42 here illustrated as comprising a generally flat plate of metal or the like. One edge 44 of the blade member extends beyond the rear edge of the heater strip 28 a short distance and is provided with a notch or slot 46. The yarn end 12 passes in contact with the under side of the heater strip and through the notch 46 in the edge of blade member 42, so

that the yarn is forced through an angular path with the base of notch 46 positioned at the apex of the angle.

The notch 46 extends into blade member 42 a distance at least equal to about the radius of the yarn and is equal in width to approximately the diameter of the yarn. The rear boundary of the notch, indicated by the reference numeral 48, is concavely curved, in a generally semi-circular manner, in the plane of the blade with the mean radius of curvature being approximately equal to the radius of the yarn, and is convexly curved in planes perpendicular to the plane of the blade. As will be seen in FIGURE 3 of the drawings, the convex radius of curvature of the rear boundary surface of notch 46 is least in the exact center of the rear boundary surface and approaches infinity at the points where the curved rear boundary surface of the notch joins the generally plane side surfaces. The plate 42 is also provided with a pair of opposed substantially conoidal grooves 50 and 52 which generally conform to the periphery of the yarn and which form guideways to and from the base of the notch 46. Grooves 50 and 52 not only result in the rear boundary surface 48 of notch 46 having a proper minimum convex radius of curvature but also provide additional restraining surfaces to force the yarn to retain its generally circular cross section.

In operation, an end of yarn 12 is threaded through the apparatus in the manner previously described to rolls 24 and the rolls are temporarily placed in operation so that the yarn may be passed to takeup means 26. Variable transformer 34 is adjusted to furnish sufiicient energy to heater strip 28 so that it is retained at the desired temperature and the takeup means 26 and the rolls 24 are then placed in operation. The apparatus there after normally requires no further attention until an end breaks or a yarn supply becomes depleted.

With reference to FIGURE of the drawings, there is illustrated a portion of a plate 54 which has been notched at 56 to provide a path for an end of yarn indicated by the reference numeral 58. Blade 54 is generally similar to the blade 42 illustrated in FIGURE 1 of the drawings except it is of sufiicient thinness that the base of notch 56, indicated by the reference numeral 60,

provides a suitable minimum radius of convex curvature without the necessity of lead-in grooves. A blade such as illustrated in FIGURE 5 has the advantage that the base 60 of notch 56 may undergo a measure of wear Without appreciably changing the radius of curvature of the angular portion of the yarn path but has the disadvantage that the restraining surfaces which force the yarn to retain a generally circular cross section are not as great in area as in the embodiment previously described.

With reference to FIGURE 6 of the drawings, there are illustrated several prior art edge-elasticized monofilaments in cross section. This figure was made by tracing a photomicrograph of sectioned 15 denier monofilament nylon yarns elasticized by drawing the same, while at an elevated temperature, over a straight edge, and the illustrated cross section is believed to be typical of prior art, edge-elasticized yarns. It will be seen that one side of the filaments, in each instance, is severely flattened, for example at 62 and 64, so that almost 30% of the peripheral surface of the yarn has a concave curvature rather than the normal convex curvature, and that the minimum diameter of the deformed filaments is, at least in some instances, less than 60% of the maximum diameter of the filament.

FIGURE 7 illustrates edge elasticized yarn according to this invention and is also a tracing from a photomicrograph of elasticized 15 denier monofilament yarn. It will be seen that the cross section of the yarn illustrated in FIGURE 7 is substantially circular, that the periphery of the yarn is not appreciably flattened at any point and that the minimum diameter of the yarn is substanitally equal to the maximum diameter of the yarn.

The new process and apparatus of this invention can be employed to elasticize any type of thermoplastic monofilament which can be elasticized by conventional edgeelasticizing procedures. Typical examples of suitable monofilaments include 7 denier nylon monofilament yarn, of either type 6, type 63 or any other type, 15 denier monofilament nylon yarn, 20 denier monofilament nylon yarn and 15 or 20 denier polyester filaments such as prepared from a product resulting from the reaction of terephthalic acid and ethylene glycol and sold under the trademark Dacron. Under certain conditions the invention can also be suitably employed for the elastization of acrylic filaments, such as those prepared from the product resulting from the polymerization of acrylonitrile or the copolymerization of acrylonitrile with a minor portion of another polymeric monomer and sold under the trademarks Acrilan and Orlon, or for the elastization of cellulose esters such as cellulose monoacetate and cellulose triacetate.

The notched blade or plate member may be formed from any suitable material which has sufiicient abrasion resistance to be satisfactorily employed in contact with the moving yarn end for a period of time. Metals, such as stainless or high-carbon steel, are generally satisfactory and this is particularly true if the metal has a sufficiently small grain size to provide a smooth yarn engaging surface at the apex of the angular portion of the yarn path. The blade member may also be made from a precious gem such as diamond or sapphire and such members have the advantages that they can be employed for exceedingly long periods of time without sufiicient wear to necessitate replacement. If a rapidly wearing material is employed for the formation of the blade, the side surfaces of the slot are soon worn to the extent that they do not force the yarn to retain a generally circular cross section and, unless one employs a blade such as illustrated in FIGURE 5 of the drawings, the minimum radius of curvature of the base of the notch may increase to the point that the blade is no longer capable of producing yarn with a satisfactory degree of elasticity.

The notch or opening in the blade member should be of a length or depth at least equal to the radius of the yarn so that the yarn is restrained against deformation through at least about half of its periphery. Its width, at the opposed points where the arcuate base joins the generally opposed sides of the notch, should be approximately equal to the diameter of the yarn to be processed and generally, in order to produce yarn having the advantages of this invention, the width of the slot at this point must be from about 80 to 120% of the diameter of the yarn and is preferably from about 90 to 110% of the diameter of the yarn being processed. The radius of curvature of the base of the slot in the plane of the blade should not vary more than 20% from the mean curvature of the periphery of the yarn and for best results should be equal to from about 90 to 110% of the mean curvature of the periphery of the yarn to be processed. For example, if the diameter of the yarn to be processed is 1.6 thousands of an inch, the mean radius of concave curvature of the base of the notch in the plane of the blade is preferably from 0.72 to 0.88 thousands of an inch.

The minimum radius of convex curvature of the arcuate base of the notch in planes perpendicular to the plane of the blade may vary within wide limits but should generally be as small as possible without resulting in the yarn being severed as it is passed through the notch in an an- The smallest possible radius of curvaturegular manner. in turn depends upon the nature of the yarn being passed over the edge, the size of the monofilament, the texture of the material from which the blade member is formed and upon the tension in the yarn. As a general rule the smaller the grain size of the material from which the blade is formed and the lower the tension in the yarn, the

smaller is the optimum minimum radius of convex curvature of the base of the slot. Also, nylon yarns may be satisfactorily run with a smaller radius of curvature than any other type of yarn and under comparable conditions a notch having about a 20% smaller minimum convex radius of curvature at the base may be used with nylon yarns than with any other type of yarns. With all factors favorable, it is sometimes possible for the base of the notch to have a minimum convex radius of curvature of from about 2 to 4 microns but under less favorable conditions a minimum radius of curvature of from about 5 to 8 microns may be required for satisfactory results. The largest minimum radius of convex curvature for the base of the notch which can satisfactorily be employed depends upon the size of the yarn being processed. The minimum convex radius of curvature should generally be no more than about 4 times the diameter of the yarn and is preferably less than the diameter of the yarn. For example, with a denier monofilament, the minimum convex radius of curvature of the base of the notch should be no greater than about 150 microns and best results are obtained if the minimum convex radius of curvature is less than about 30 microns.

The blade member may be of any desired thickness and by the provision of lead-in grooves, such as illustrated in FIGURES l to 4 of the drawings, may have a thickness appreciably greater than twice the desired minimum radius of convex curvature utilized at the base of the notch. A common razor blade, for example, readily provides a satisfactory blank from which the blade member can be constructedor one can utilize shim stock or the like having approximately the thickness desired. For manufacturing a blade member such as illustrated in FIGURE 5 of the drawings, shim stock having a thickness of from about 0.5 thousands to 2 thousands of an inch may suitably be employed and the necessity of lead-in grooves eliminated. A notch having the desired shape can readily be formed in the edge of a plate member by first rounding one edge of a piece of shim stock or other thin metal having a thickness corresponding to the diameter of the yarn to be processed and using the rounded edge of the shim stock as a file to grind the notch and, where desired, the lead-in grooves. Of course, if the blade is to be formed of diamond, sapphire or similar material, the services of a skilled stone cutter are generally required.

The angle of approach and the angle of departure of the yarn to and from the blade member may be conventional and the included angle between the approaching and departing yarn may vary from about .to about 10 or even less if the angle of grind on the blade member permits. As a general rule, the smaller the included angle between the approaching and departing yarn, the higher the degree of elastization obtained, but in some instances it may be advantageous to make the angle of approach relatively large, for example from 30 to 100, so that the yarn may be more readily heated to a proper temperature at the time it contacts the blade edge.

The tension in the yarn passing about the blade member and the temperature of the yarn at the time it contacts the blade edge may likewise be conventional and will depend upon the type of yarn being processed and the particular procedure of elastization being utilized. Under proper conditions the temperature of the yarn may vary from room temperature up to the sticking temperature of the yarn and the tension in the yarn may vary from about .05 to 2.5 grams per denier. The linear velocity of the yarn about the blade edge may also be conventional and may vary from substantially Zero yards per minute up to as much as one thousand yards per minute in some instances.

Except for its round cross section and the advantages derived therefrom, the yarn of this invention is generally similar to prior art edge-elasticized yarn. The yarn immediately following its passage about the blade member is generally characterized by a loosely coiled appearance, when in an untensioned condition, and. if the yarn is untwisted and is not torsionally stressed in some other manner, the loops generally form so that about 50% are in one direction and the remaining half of the loops are in the opposite direction with reversal points randomly spaced along the length of the yarn. On the other hand, if the yarn is intentionally stressed in a torsional manner, the loops will form so that they are all running in the same direction. As in other types of edge-elasticized yarn, the stresses created by running the yarn about the blade member are largely latent in nature and must be thermally relaxed in order for the yarn to develop its full elastic nature. Procedures for thermally relaxing the latent stresses in edge-elasticized yarns, either before or after the yarn is formed into fabrics, are now well known in the art and for this reason will not be discussed in detail in this specification,

Having thus described my invention what I desire to claim and secure by Letters Patent is:

1. Apparatus for elasticizing an end of monofilament yarn which comprises in combination a yam supply means, a yarn take-up means for withdrawing an end of yarn from said supply means and transporting the same under tension over a linear path, a blade member positioned in the yarn path and about which the yarn is drawn to cause it to follow an acutely angular course, said blade member having an opening therein to receive the yarn with one boundary surface of said opening providing a yarn engaging surface, arcuate in a plurality of planes, positioned at the apex of the angle in the yarn path, said yarn engaging surface being concavely arcuate in Planes parallel to the plane of said blade member such that when a monofilament, having a cross sectional radius selected to approximately correspond to the minimum radius of concave curvature of said yarn engaging surface, is passed in an angular manner about said yarn engaging surface, said monofilament while in contact with said yarn engaging surface is laterally restrained to prevent cross sectional deformation, and said yarn engaging surface being convexly arcuate in planes perpendicular to the plane of said blade member, the mean radius of convex curvature in a plane bisecting said yarn engaging surface being not greater than microns.

2. Apparatus for elasticizing an end of monofilament yarn which apparatus comprises a blade member having an opening therein to act as a guideway for forcing an end of yarn under tension through an acutely angular path, one boundary surface of said opening being smoothly arcuate in two planes normal to one another, the curvature of said surface in one plane being concave and such that during such time as the yarn is being passed through the angular portion of the yarn path, it is forced to retain a generally circular cross section, and the curvature of said boundary surface in planes perpendicular to said one plane being smoothly convex and such that as the yarn is drawn in contact therewith, the yarn is forced through an arcuate path having a minimum radius of curvature of not more than about 4 times the diameter of the yarn.

3. Apparatus according to claim 2 wherein said member is a plate and said opening is a U-shaped notch in one edge of said plate,

4. Apparatus according to claim 3 wherein said plate is Provided on opposite faces thereof with a pair of opposed, smooth concavely arcuate grooves, leading tothe base of said notch, to act as guideways for the yarn entering and leaving said notch and to provide additional peripheral restraint against cross-sectional deformation of the yarn.

5. Apparatus for elasticizing an end of monofilament yarn which comprises a plate having a U-shaped notch in one edge thereof, the boundary surface of said notch removed from said one edge having a curvature in the plane of the plate approximately conforming to the periphery of the yarn to be processed, said plate also being provided with opposed, substantially conoidal grooves on the faces thereof, said grooves generally conforming to the periphery of said yarn and forming guideways to and from said notch for an end of yarn being drawn therethru, said boundary surface of said notch being rounded so that it is arcuate in a smooth convex curve in planes perpendicular to the plane of the plate, and the depths of said grooves, as they enter said notch, being such that the minimum mean radius of convex curvature of said boundary surface in a plane perpendicular to the plane of the plate is not more than about 4 times the width of said notch.

6. A blade member for use in apparatus for edgeelasticizing thermoplastic yarns comprising a plate having an opening therein providing a boundary surface for slidably engaging an end of yarn, said boundary surface having a smooth curved concavely arcuate configuration in planes parallel to the plane of said plate such that when a monofilament, selected to have a cross sectional radius approximately equal to the minimum radius of concave curvature of said boundary surface, is passed in an acutely angular path about said surface with said surface being disposed at the apex of the angle in the yarn path, said monofilament while in contact with said boundary surface is laterally restrained to prevent cross sectional deformation, and said boundary surface having a smooth curved convexly arcuate configuration in planes perpendicular to the plane of said plate, the mean radius of convex curvature in a plane intersecting said boundary surface at a point of maximum concave curvature being not greater than 150 microns.

7. A blade member according to claim 6 wherein said opening is a U-shaped notch in one edge of said plate.

8. A blade member according to claim 7 wherein the minimum radius of convex curvature of the boundary surface of said notch is not greater than 30 microns.

9. A blade member for use in apparatus for edgeelasticizing thermoplastic yarns comprising a plate having a U-shaped notch in one edge thereof, the bottom of said notch providing a boundary surface for engaging an end of yarn, said boundary surface having a smooth curved convexly arcuate configuration with a minimum radius of convex curvature equal to not more than 4 times the width of said notch, whereby when an end of yarn is drawn in an acutely angular path through said notch with said boundary surface disposed at the apex of the acute angle in the yarn path, said yarn is strained beyond its elastic limit as a result of being conformed to said convex curvature and is circumferentially restrained against cross sectional deformation by the configuration of said notch.

10. A blade member according to claim 9 wherein said boundary surface at the base of said notch has a minimum radius of convex curvature of not more than about 30 microns.

11. A blade member according to claim 10 wherein said plate is provided with opposed, substantially conoidal guide grooves leading to and away from the base of said notch.

12. In an apparatus for edge-elasticizing an end of monofilament yarn, the combination with a yarn supply means, a yarn takeup means, and means for withdrawing an end of yarn from said supply means and transporting the same under tension over a linear path; of a blade member having an opening therein providing a boundary surface for slidably engaging said yarn, said boundary surface being concavely arcuate in planes parallel to the plane of said blade member such that said yarn engaging boundary surface is generally semi-circular in con- .guration, said boundary surface having a smooth curved convexly arcuate configuration in planes perpendicular to the plane of said blade member, the minimum radius of convex curvature being equal to not more than the width of said opening, and means to guide said yarn in an acutely angular path such that said boundary surface is disposed at the apex of the acute angle in the yarn path.

13. A combination according to claim 12 wherein said opening is a U-shaped notch and said minimum radius of convex curvature is equal to not more than 30 microns.

References Cited in the file of this patent UNITED STATES PATENTS 414,090 Taylor Oct. 29, 1889 1,330,534 Hertel et a1 Feb. 10, 1920 2,041,798 Taylor May 26, 1936 2,169,270 McNally Aug. 15, 1939 2,197,896 Miles Apr. 23, 1940 2,245,874 Robinson June 17, 1941 2,326,174 Rutishauser Aug. 10, 1943 2,334,420 Lang Nov. 16, 1943 2,475,922 Stockly July 12, 1949 2,477,909 Stockly Aug. 2, 1949 2,597,577 Drisch et, a1 May 20, 1952 2,623,266 Hemmi Dec. 30, 1952 2,668,430 Laros Feb. 9, 1954 2,751,661 Shattuck June 26, 1956 2,875,502 Matthews et al Mar. 3, 1959 FOREIGN PATENTS 164,127 Australia July 15, 1955 522,045 Belgium Feb. 10, 1954 

